Conventional oligonucleotide synthesis entails first binding the protected 3′ terminal nucleotide to a solid support by an ester linkage. The oligonucleotide is extended from the 3′ end by the addition of an appropriate sequence of additional protected bases. In other words, the 3′ end of a nucleotide is attached to the 5′ end of the elongating oligonucleotide. This process yields an oligonucleotide bound to the support at its 3′ end. The oligonucleotide is then deprotected, which results in cleavage from the support, and then purified.
U.S. Pat. No. 3,890,417 describes a method for making a porous diaphragm suitable for use in electrolytic cells. The diaphragm is formed as a sheet from aqueous polytetrafluoroethylene (PTFE) suspension and a solid, non-porous particle additive. Porosity is imparted to the product by removal of the particulate additive. U.S. Pat. No. 4,153,661 describes a similar method for making high tensile strength PTFE composite sheet material from aqueous PTFE suspension, and organic or inorganic particles which comprises mixing and calendering at an elevated temperature (50–100° C.) to produce a self-supporting film for use as an electronic insulator. U.S. Pat. Nos. 4,373,519; 4,460,642; 4,565,663 and 4,971,736 disclose methods for making water-swellable composite sheets having hydrophilic, absorptive particles enmeshed in the PTFE matrix for use as wound dressing and chromatographic supports.
In each instance for oligonucleotide synthesis, it is important to provide a substrate solid phase material that contains terminal OH groups available to start a coupling reaction and that each synthesis step for the coupling reaction to create an oligomer (i.e., deprotection and capping) goes to completion.